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56
RADIATION CHEMISTRY AND PHYSICS, RADIATION TECHNOLOGIES
Fig.3. Comparison of DSC curves recorded for the reference
alpha globulins (subjected to water treatment)
and for the products irradiated with 2.5 and 24 kGy
doses.
were clearly more significant. The bigger exothermal
effects were thus accompanied by the second
and the third stages of the irradiated samples decomposition
as compared to the reference ones,
while the smaler exothermal effects correspond to
the first decomposition stage (Figs.2 and 3). Moreover,
participation of IB, IIB and IIIB effects became
more significant in DSC curves of the irradiated
products. Results of thermogravimetry
have shown that in the cases of irradiated products
the mass loss was smaller in the first stage of
decomposition and bigger in the second and third
stages, in comparison to the reference samples. For
example, in the case of the reference gamma globulins
mass loss reach 59.98, 31.88 and 8.66% during
the first, second and third decomposition stages.
The appropriate values obtained for the sample
irradiated with 2.5 kGy dose were equal to 52.29,
34.64 and 12.05% and those found for the sample
irradiated with 24 kGy were equal to 40.00, 45.06
and 12.95%, respectively. Moreover, mass loss in
the IB stage was also larger in relation to that obtained
in IA stage in the cases of irradiated than
in the case of non-irradiated samples. Therefore,
Fig.4. Comparison of DSC effects connected to the last fast
stage of decomposition of the irradiated native dry
globulins and the initial gamma globulins.
the reference sample loses 50.65 and 9.33% of mass
during the IA and IB stages, respectively, while the
irradiated samples loses respectively 26.53 and
22.96% (irradiated with 2.5 kGy) and 19.75 and
20.25% (irradiated with 24 kGy). This was accompanied
by the smaller DTG effect corresponding
to the first decomposition stage and the bigger one
corresponding to the second stage (Fig.1).
The results are related to the modification of
amino-acid composition and modification of proteins
tertiary structure. In particular, increase in the
temperature of particular processes taking place
during decomposition of the irradiated proteins
demonstrates the occurring crosslinking processes.
It is because that the first stage of decomposition
consist on the cleavage of polypeptide linkages and
shifts to the higher temperature in result of disulfide
bridges formation [1]. On the contrary, decrease
of decomposition temperature gives evidence
of degradation induced by gamma irradiation
performed for solid native proteins.
The relatively large differeces between decomposition
of the irradiated and non-irradiated
samples were detected by DSC and thermogravimetry
already after irradiation of water suspensions
with a dose of 2.5 kGy (Figs.1-3).
References
[1]. Bihari-Varga M.: J. Therm. Anal., 23, 7-13 (1982).
[2]. Cieśla K., Roos Y., Głuszewski W.: Radiat. Phys.
Chem., 58, 233-243 (2000).